In many situations, it may be desirable to sample fluid from a fluid source without exposing the fluid to the surrounding environment. For example, during pre-flight inspections of their aircraft, pilots are required to visually inspect the fuel within the fuel system for the correct octane rating and for the presence of water and other visual contamination. Aircraft manufacturers typically install fuel drain valves at appropriate locations within an aircraft's fuel system. These drain valves are generally located on the bottom side of the aircraft's wings, fuselage and fuel filter, particularly at the lowest point within these locations.
Known drain valves require a cup or bottle to catch the fuel flowing from the valve's drain port, which exposes the pilot and surrounding environment to both liquid fuel and fuel vapor. Known drain valves also require the sampled fuel to be disposed of onto the tarmac or manually recycled back into the fuel tank through the fuel tank inlet. None of these drain valves permit the fuel to be returned to its source back through the drain valve. Moreover, none of these drain valves permit back flow to flush debris or contaminants trapped within the valve. Typically, the only way to clear debris from within the drain valve is to continue taking additional fluid samples and/or completely remove the drain valve from the aircraft and then clean.